There is known an alignment apparatus for aligning an object, such as a substrate, in various apparatuses, such as an exposure apparatus, and the like. Examples of an alignment apparatus include one having a fine adjustment stage, which moves at a high precision on an X-Y stage, which moves with a long stroke (see, for example, Japanese Patent Laid Open No. 2000-106344). The fine adjustment stage can employ, e.g., an electromagnetic actuator in which electromagnets and magnetic bodies are so arranged as to face each other and generate an attraction force between them as an actuator for finely moving a wafer top plate (stage).
FIGS. 13A to 13D are schematic views showing the arrangement of an electromagnetic actuator. FIGS. 13A and 13B are top views; and FIGS. 13C and 13D, side views. An electromagnetic actuator shown in FIGS. 13A to 13D is made up of an electromagnet 508 formed by winding a coil 586 around the central tooth of an E magnetic body 585, and a magnetic body 507 arranged to face the attraction surface of the electromagnet 508.
If a current is supplied to the coil 586 of the electromagnet 508, a magnetic field is generated. The magnetic force of the magnetic field attracts the magnetic body 507 toward the electromagnet 508. At this time, the magnetic body 507 receives an attraction force mainly in a direction A, which reduces an interval between the magnetic body 507 and the electromagnet 508, as shown in FIG. 13A. If the central axis of the electromagnet 508 and that of the magnetic body 507 have a relative positional shift in the lateral direction, as shown in FIG. 13B, intervals between the magnetic body 507 and the left and right sides of the E magnetic body 585 are non-uniform. The left side, which has a smaller interval to the magnetic body 507, generates a larger attraction force. This generates a force in a lateral direction B so as to further reduce the interval on the left side. At the same time, a small rotational force is generated.
Also, if the central axis of the electromagnet 508 and that of the magnetic body 507 are not parallel to each other, a rotational force acts in a rotational direction C, which reduces an interval to the electromagnet 508. At the same time, a small translational force is generated in the central axial direction.
This non-uniformity in interval between the electromagnet 508 and the magnetic body 507, which may generate an attraction force in an undesirable direction, can be caused by a mechanical factor such as an assembly error. The non-uniformity can also be caused by driving a wafer top plate (stage) to a target position. Such a force may cause a disturbance in an alignment apparatus, and thus may degrade the performance, i.e., decrease the alignment precision and lengthen the settling time.